Astroparticle Physics

The research in the field of Astroparticle Physics at KVI-CART focuses on the study of the sky map of the high-energy Universe, addressing the unknown origin of cosmic rays at the highest energies. Cosmic rays are a collective name for a variety of subatomic particles that are continuously bombarding the outer layers of the Earth’s atmosphere. While the Sun is a well-known source of low-energy cosmic rays, the origin of particles with energies in excess of 1012 eV is still an open question. Supernovae explosions, for instance, are commonly believed to be the source of cosmic rays with energies up to 1015 eV, but so far it has not been possible to prove this observationally. Beyond this energy domain cosmic-ray particles must originate from unknown extragalactic sources at very large distances. Some of these particles are reaching energies well in excess of the highest energies that can be produced in the most advanced man-made particle accelerators. In fact, cosmic rays are the only observed ultra-high energy (UHE) particles on Earth, i.e. with energies in excess of 1016 eV. Still, the acceleration mechanism(s) leading to such ultra-high energies and their sources remain largely unknown.

Another source for cosmic radiation, in particular neutrinos, could be the annihilation of dark matter particles. There is a variety of topics that are addressed in astroparticle physics, among which

Physics in energetic astronomical processes that may lead to the production of ultra-high energy particles.

Physics in particle cascades in the atmosphere and the emission of electromagnetic radiation of radio frequencies.

Although lightning is being studied for more than 250 years, the details of the lightning mechanisms are still unknown.

With the advent of digital radio detection arrays, such as the LOFAR instrument a new window has been opened which allows precision measurements of the initial steps in lightning initiation and propagation.

In a recent study, we have shown that the radio measurements of the particle shower can be used to study the strength and the direction of the electric fields in the atmosphere. The determined electric fields can be correlated with the structure of the part of the thundercloud that is probed.

Stills from a video by Tom A. Warner showing lightning propagation taken with a high-speed camera (see https://vimeo.com/28457062)

The Astroparticle physics group at KVI-CART is involved in theoretical as well as experimental research at LOFAR, The Pierre Auger Observatory (PAO), KM3NET, and CTA.